Lefkowitz R J, Roth J, Pastan I
Science. 1970 Nov 6;170(3958):633-5. doi: 10.1126/science.170.3958.633.
Biologically active iodine-125-labeled adrenocorticotropic hormone (ACTH) binds specifically to ACTH receptors extracted from adrenals. Unlabeled ACTH at 1 picogram per milliliter significantly displaces labeled ACTH from these receptors. This system, which appears to be applicable to all polypeptide hormones, provides a rapid and sensitive method for measurements of biologically active ACTH in dilute whole plasma.